In the production of fermented dairy products, such as yoghurt, cream cheese, cottage cheese etc. functional and/or organoleptic properties, as well as nutritional value are of importance. Among the organoleptic properties sourness, firmness and mouthfeel of the dairy product is of great importance for customer acceptance. Moreover, there are differences in customer acceptance based on national and cultural differences, which fact requires these properties to be adjustable.
Many efforts have been exercised in order to generate dairy products of nutritional value and with improved functional and/or organoleptic properties, including acidified, edible gels on milk basis. A typical example of such products is desserts, especially yoghurt and curd. In order to prepare such products of satisfactory quality, it is today necessary to ferment dairy ingredients (whole or low fat milk, skim milk, condensed milk, and dried skim milk) using bacterial cultures. Some of these may be indigenous to milk or introduced during processing. Fermentation not only reduces pH of the milk, but also results in the smooth, viscous liquid or soft curd characteristic of yoghurts. Stabilizers and sweeteners are often added during processing to modify texture and/or prevent syneresis as well as reduce intensity of the tart or sour flavor (Kosikowski & Mistry: Cheese and fermented milk products). For example, Swiss-style yoghurt uses large amounts up to 0.75% of stabilizer to obtain products of high viscosity.
In many fermented dairy products, particularly yoghurt products, firmness and sourness are of great importance. E.g. yoghurt is a soft-textured product where texture and sourness are of specific importance for the final product to be used, eaten as such, or used in a prepared ready-to-eat form. Metabolic activity of the bacterial cultures generate volatile flavor compounds such as acetic acid, diacetyl, and acetaldehyde which coupled with the acidity contribute to the unique sour or tart flavor characteristic of yoghurts. However, the tartness or sourness may be too intense and may need to be reduced by adding sweeteners. Another unique characteristic of yoghurt is its viscosity and smooth mouthfeel. The occurrence of syneresis during storage releases whey from the smooth gel matrix resulting in significant changes in texture. Hence the addition of stabilizers to prevent or control syneresis. Excessive addition of stabilizers, however, could also make the product too viscous adversely affecting mouthfeel and taste.    Wright and Rand, 1973; J. Food Sci. 38: 1132–1135 discloses enzymatic conversion of lactose to lactobiotic acid and its use to acidify milk.    Lin et al., 1993; Biotech. Adv. 11: 417–427 discloses the use of an oligosaccharide oxidase to convert lactose to lactobionic acid in a wheat bran substrate.    Satory et al., 1997; Biotechnol. Lett. 19:1205–1208 discloses the use of glucose-fructose oxidoreductase (GFOR) for the conversion of lactose to lactobionic acid.
None of these references discusses the use of enzymatic conversion of lactose to lactobionic acid for affecting functional and/or organoleptic properties, such as firmness and sourness of a dairy product.
Thus, there is a need for an improved method for the preparation of fermented dairy products, in particular a method for providing dairy products having improved functional and/or organoleptic properties.
One object of the present invention is to provide a method for the preparation of a fermented dairy product having improved firmness. Specifically, it is an object to provide a less firm fermented dairy product.
Another object of the present invention is to provide a method for the preparation of a fermented dairy product having improved taste. Specifically, it is an object to provide a less sour fermented dairy product.
A still further object of the present invention is to provide a method for affecting firmness and sourness of a fermented dairy product. Specifically, it is an object to provide a less firm and less sour fermented dairy product.